docs: def get_file(self, filename, scope='all'):
          ''' Returns the BIDSFile object with the specified path.
  
          Args:
              filename (str): The path of the file to retrieve. Must be either
                  an absolute path, or relative to the root of this BIDSLayout.
              scope (str, list): Scope of the search space. If passed, only
                  BIDSLayouts that match the specified scope will be
                  searched. See BIDSLayout docstring for valid values.
  
          Returns: A BIDSFile, or None if no match was found.
          '''
          filename = os.path.abspath(os.path.join(self.root, filename))
          layouts = self._get_layouts_in_scope(scope)
          for ly in layouts:
              if filename in ly.files:
                  return ly.files[filename]
          return None